Method and apparatus for allocating a beacon signal in a wireless communications network

ABSTRACT

A method and apparatus for transmitting beacon signals in a wireless communications network. For a given cell site, a single frequency may be used for the beacon signal by assigning different beacon signal time slots to different sectors of the cell site. During one time slot, the beacon signal is transmitted to one of the sectors, and during another one of the time slots, the beacon signal is transmitted to a different one of the sectors. Because a single frequency can be used for all of the sectors of a cell site, more frequencies are available for other purposes, such as for user traffic, for example. The invention improves spectral efficiency, reduces adjacent channel interference and co-channel interference and allows power consumption to be controlled.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/973,623, filed Oct. 26, 2004, entitled “METHOD AND APPARATUS FORALLOCATING A BEACON SIGNAL IN A WIRELESS COMMUNICATIONS NETWORK”, theentirety of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to communications networks and, more particularly,to a method and apparatus for allocating beacon signals in acommunications network.

2. Description of Related Art

In wireless communications networks, beacon signals, which are sometimesalso referred to as pilot signals, are broadcast over the airwaves toenable mobile devices to search for cell sites that are handoffcandidates. Generally, one beacon signal is required for each sector ofeach cell site and each beacon signal of a given cell site uses adifferent frequency. FIG. 1 is a diagram of a plurality of cell sites,each of which is divided into three sectors with each sector of a givencell site using a different frequency. The frequencies that areallocated for use as beacon signals for the network are frequencies f₁through f₁₂. For cell site 1, which is shown in block diagram form inFIG. 2, the beacon signal for sector a uses frequency f₁ and isbroadcast over the sector by directional antenna 11. The beacon signalfor sector p uses frequency f₂ and is broadcast over the sector bydirectional antenna 12. The beacon signal for sector y uses frequency f₃and is broadcast over the sector by directional antenna 13. The nextadjacent cell site 2 uses frequency f₄ for sector a, frequency f₅ forsector p and frequency f₆ for sector y. The next adjacent cell site 3uses frequency f₇ for sector a, frequency f₅ for sector 13 and frequencyf₉ for sector y. The next adjacent cell site 4 uses frequency f₁₀ forsector a, frequency f₁₁ for sector [3 and frequency f₁₂ for sector y.

After frequencies f₁ through f₁₂ have been used for the beacon signalsfor cell sites 1 through 4, those frequencies are then reused innon-adjacent cells. For example, cell site 1, which uses frequencies f₁through f₃ for the beacon signals is separated from cell site 5, whichalso uses frequencies f₁ through f₃ for the beacons signals, by cellsite 4, which uses frequencies f₁₀ through f₁₂ for the beacons signals.As the number of frequencies used for the beacon signals increases, thepossibility that co-channel interference will occur decreases. However,increasing the number of frequencies that are reserved for the beaconsignals decreases the number of frequencies that can be used for callertraffic. Therefore, with the current beacon signal allocation scheme, atradeoff exists between spectral efficiency and co-channel interference.

It can be seen from FIG. 1 that each cell site uses three differentfrequencies for the beacon signals and that the beacon signalfrequencies are reused after twelve frequencies have been used. Afterfrequencies f₁ through f₁₂ have been used for the beacon signals forcell sites 1 through 4, those frequencies are then reused innon-adjacent cells. For example, cell site 1, which uses frequencies f₁through f₃ for the beacon signals is separated from cell site 5, whichalso uses frequencies f₁ through f₃ for the beacons signals, by cellsite 4, which uses frequencies f₁₀ through f₁₂ for the beacons signals.Therefore, in the beacon signal frequency allocation scheme shown inFIG. 1, twelve frequencies are allocated to four cell sites. This iscommonly referred to as a 4/12 beacon signal allocation configuration,where X=4 corresponds to the number of cell sites that use a givenfrequency before the frequency is reused and Y=12 corresponds to thetotal number of frequencies used. Other beacon signal frequencyallocation schemes that are common are 5/15 and 7/21.

FIG. 2 is a functional block diagram of cell site 1 shown in FIG. 1. Asshown in FIG. 2, the user frequencies start at frequency f₁₃ becausefrequencies f₁ through f₁₂ are reserved for the beacon signals. Forexemplary purposes, FIG. 2 depicts only three frequencies (f₁₃ throughf₁₅) being used for caller traffic and the same user frequencies beingused for caller traffic for all of the sectors. The beacon signals arecontinuously broadcast by the base stations of the cell sites atconstant power so that the mobile devices are able to easily detect thebeacon signals. In order to avoid interference, the frequencies that areused for the beacon signals are not used for caller traffic. Typically,frequency hopping is used so that the same frequency is not beingtransmitted at the same time in two sectors of the same cell site. Forexample, if user frequencies f₁₃ and f₁₄ are being transmitted oversector α by antenna 11 in time slots t₁ and t₂, respectively, userfrequencies f₁₄ and f₁₃ may be transmitted over sector β by antenna 12in time slots t₁ and t₂, respectively, but not in time slots t₂ and t₁,respectively.

A signal combining and distribution unit 10 receives the beacon signalsgenerated by beacon logic 14 and caller traffic signals generated bycaller traffic logic 15. The signal combining and distribution unit 10combines the beacon and caller traffic signals for broadcasting by therespective antennas 11, 12 and 13 over the respective sectors, α, β andγ. The beacon signals are normally broadcast in time slot t₁ of aBroadcast Common Control Channel (BCCH) frame that is made up of eighttime slots of equal duration, t₁ through t₈. For this reason, the beaconlogic 14 is referred to herein as BCCH logic.

FIG. 3 depicts a BCCH frame 21. The first time slot, which correspondsto t₁, is reserved for transmission of BCCH information, which includesthe beacon signal. Time slots t₂ through t₈ can be used to transmitinformation other than BCCH information, including caller traffic.However, even when there is no caller traffic, all eight time slots t₁through t₈ are transmitted so that mobile devices can detect the beaconsignal. In order to ensure that mobile devices can easily detect thebeacon signal, the BCCH frame 21 is continuously broadcast.

One of the disadvantages of allocating beacon signals in the mannerdescribed above with reference to FIGS. 1-3 is that a relatively largenumber of frequencies must be reserved for use as beacon signals, whichreduces the spectral efficiency of the network. For example, withrespect to the configuration shown in FIG. 1, twelve frequencies arereserved for the beacon signals. If these frequencies were not reservedfor use as beacon signals, they could be used for other purposes, suchas caller traffic, which would allow each cell site to service morecalls. Therefore, allocating a large number of frequencies for use asthe beacon signals reduces the number of calls that can be handled byeach cell site, thereby reducing network coverage and increasing overallnetwork costs.

Another disadvantage of the current beacon signal allocation scheme isthat transmission of the BCCH frame even when there is no caller trafficis inefficient in terms of power consumption. In addition, because thefirst time slot t₁ is reserved for transmission of the BCCH frame, thefirst time slot cannot be used for other purposes, such as for callertraffic. For this additional reason, the current scheme of beacon signalfrequency allocation is not spectrally efficient.

Another disadvantage of the current beacon signal allocation scheme isthat it requires time consuming and tedious frequency planning to ensurethat all BCCH channels in the same cell site have sufficient frequencyseparation to avoid adjacent channel interference impact (i.e.,interference between the signals in adjacent sectors of the same cellsite). In addition, sufficient distance separation is necessary toreduce co-channel interference. As shown in FIG. 1, cell sites that usethe same frequencies for the beacon channels are not located adjacentone another, but are separated by some distance. This is becauseco-channel interference will result if cell sites that use the samefrequencies are located adjacent one another. The frequencies used forthe beacon signals and the locations of the cell sites are chosen sothat co-channel interference is reduced to acceptable levels.

Accordingly, a need exists for a method and apparatus for beacon signalallocation that provide a spectrally efficient way of performing beaconsignal allocation that is also efficient in terms of power consumption.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus areprovided for transmitting beacon signals in a wireless communicationsnetwork. For a given cell site, a single frequency may be used for thebeacon signal by assigning different beacon signal time slots todifferent sectors of the cell site. During one time slot, the beaconsignal is transmitted to one of the sectors, and during another one ofthe time slots, the beacon signal is transmitted to a different one ofthe sectors. Because a single frequency can be used for all of thesectors of a cell site, more frequencies are available for use for usertraffic. Therefore, the invention improves spectral efficiency. Inaddition, because a lesser number of frequencies are needed for thebeacon signals, adjacent channel interference and co-channelinterference are reduced. Also, time slots for the beacon signals can beallocated to the sectors in any desired manner. This allows time slotsthat are not being used for beacon signals to be used for otherpurposes, such as for caller traffic, for example, which furtherimproves spectral efficiency. Time slots can also be allocated in a waythat allows power consumption to be controller. For example, in a sectorwhere there is very little caller traffic, less beacon signal time slotscan be allocated, which reduces power consumption.

In accordance with one embodiment, the apparatus of the inventioncomprises beacon signal logic configured to allocate at least a firstbeacon signal time slot t₁ to at least the first sector α, and atransmitter that transmits a first beacon signal on a first beaconsignal frequency f₁ over the first sector α during the first beaconsignal time slot t₁.

In accordance with another embodiment, the apparatus comprises beaconsignal logic and a transmitter. The beacon signal logic is configured toallocate at least a first beacon signal time slot t₁ to the first sectorα, a second beacon signal time slot t₂ to the second sector β, and athird beacon signal time slot t₃ to the third sector γ. The transmittertransmits a first beacon signal on a first beacon signal frequency f₁over the first sector α during time slot t₁, a second beacon signal onthe first beacon signal frequency f₁ over the second sector β during thesecond time slot t₂, and a third beacon signal on the first beaconsignal frequency f₁ over the first sector γ during the third time slott₃. Time slot t₂ occurs later in time than time slot t₁ and time slot t₃occurs later in time than time slot t₂.

In accordance with another embodiment, the apparatus comprises beaconsignal logic configured to sequentially allocate beacon signal timeslots to the first sector α, the second sector β and the third sector γ,and a transmitter that transmits beacon signals on a first beacon signalfrequency f₁ over the first sector α, the second sector β and the thirdsector γ during respective time slots. When the beacon signal is beingtransmitted over sector α, the beacon signal is not being transmittedover sectors β or γ. When the beacon signal is being transmitted oversector β, the beacon signal is not being transmitted over sectors α orγ. When the beacon signal is being transmitted over sector γ, the beaconsignal is not being transmitted over sectors β or α.

In accordance with another embodiment, the apparatus comprises beaconsignal logic configured to randomly or pseudo-randomly allocate beaconsignal time slots to the first sector α, the second sector β and thethird sector γ, and a transmitter that transmits beacon signals on afirst beacon signal frequency f₁ over the first sector α, the secondsector β and the third sector γ during respective time slots allocatedto the respective sectors.

The present invention also provides a method for allocating beaconsignals. In accordance with one embodiment, the method comprisesallocating at least a first beacon signal time slot t₁ to at least thefirst sector α, and transmitting a first beacon signal on a first beaconsignal frequency f₁ over the first sector α during the first beaconsignal time slot t₁.

In accordance with another embodiment, the method comprises allocatingat least a first beacon signal time slot t₁ to the first sector α, asecond beacon signal time slot t₂ to the second sector β, and a thirdbeacon signal time slot t₃ to the third sector γ, and transmitting afirst beacon signal on a first beacon signal frequency f₁ over the firstsector α during time slot t₁, a second beacon signal on the first beaconsignal frequency f₁ over the second sector β during the second time slott₂, and a third beacon signal on the first beacon signal frequency f₁over the first sector γ during the third time slot t₃. Time slot t₂occurs later in time than time slot t₁ and time slot t₃ occurs later intime than time slot t₂.

In accordance with another embodiment, the method comprises sequentiallyallocating beacon signal time slots to the first sector α, the secondsector β and the third sector γ, and transmitting beacon signals on afirst beacon signal frequency f₁ over the first sector α, the secondsector β and the third sector γ during respective time slots. When thebeacon signal is being transmitted over sector α, the beacon signal isnot being transmitted over sectors β or γ. When the beacon signal isbeing transmitted over sector β, the beacon signal is not beingtransmitted over sectors α or γ. When the beacon signal is beingtransmitted over sector γ, the beacon signal is not being transmittedover sectors β or α.

In accordance with another embodiment, the method comprises randomly orpseudo-randomly allocating beacon signal time slots to the first sectorα, the second sector β and the third sector γ, and transmitting beaconsignals on a first beacon signal frequency f₁ over the first sector α,the second sector β and the third sector γ during respective time slotsallocated to the respective sectors.

The present invention also provides a computer program for allocatingbeacon signals. In accordance with one embodiment, the program comprisesa first code segment for allocating at least a first beacon signal timeslot, t₁, to at least the first sector α, and a second code segment forcausing a first beacon signal to be transmitted on a first beacon signalfrequency, f₁, over the first sector α during the first beacon signaltime slot t₁.

In accordance with another embodiment, the program comprises a firstcode segment for allocating at least a first beacon signal time slot t₁to the first sector α, a second beacon signal time slot t₂ to the secondsector β, and a third beacon signal time slot t₃ to the third sector γ,and a second code segment for causing a first beacon signal to betransmitted on a first beacon signal frequency f₁ over the first sectorα during time slot t₁, a second beacon signal to be transmitted on thefirst beacon signal frequency f₁ over the second sector β during thesecond time slot t₂, and a third beacon signal to be transmitted on thefirst beacon signal frequency f₁ over the first sector γ during thethird time slot t₃. Time slot t₂ occurs later in time than time slot t₁and time slot t₃ occurs later in time than time slot t₂.

These and other features and advantages of the invention will becomeapparent from the following description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram of a plurality of cell sites, each of whichis divided into three sectors with each sector of a given cell siteusing a different frequency.

FIG. 2 illustrates a functional block diagram of one of the cell sitesshown in FIG. 1.

FIG. 3 illustrates a BCCH frame having eight time slots, wherein thefirst time slot is used for beacon signal transmission.

FIG. 4 illustrates a pictorial diagram of a plurality of cell sites,each of which is divided into three sectors, α, β and γ, with all of thesectors of a given cell site using the same frequency for the beaconsignal.

FIG. 5 illustrates a functional block diagram of one of the cell sitesshown in the diagram of FIG. 4.

FIG. 6 illustrates the distribution of beacon signals to sectors α, βand γ of one of the cell sites shown in FIG. 5.

FIG. 7 illustrates a timing chart that demonstrates an example of themanner in which three frames of beacon signals are transmittedsequentially over three different sectors of a cell site using the samefrequency in accordance with the invention.

FIG. 8 illustrates a timing chart that demonstrates an example of themanner in which three frames of beacon signals are transmitted randomlyover three different sectors of a cell site using the same frequency inaccordance with the invention.

FIG. 9 illustrates a flow chart describing the method of the presentinvention in accordance with an exemplary embodiment.

FIG. 10 shows an alternative embodiment of cell site 30 shown in FIG. 4that enables the beacon signal to bypass the combining and distributionunit.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In accordance with the preferred embodiment of the present invention, asingle frequency is allocated for the beacon signal for each cell site.FIG. 4 is a diagram of a plurality of cell sites, each of which isdivided into three sectors, α, β and γ, with all of the sectors of agiven cell site using the same frequency for the beacon signal for thatsite. This diagram represents an example of the manner in whichfrequencies can be allocated in accordance with the method of theinvention. The beacon signal allocation configuration represented by thediagram shown in FIG. 4 is a 1/3 beacon signal frequency allocationscheme, where X=1 corresponds to the number of cell sites that use agiven frequency for the beacon signal and Y=3 corresponds to the totalnumber of frequencies used for the beacon signals for the network.

It should be noted that the invention is not limited to the 1/3 beaconsignal frequency allocation scheme shown in FIG. 3. Other allocationschemes may be used, such as, for example, 1/4, 4/12, 7/21 and 5/15. Forease of discussion and illustration, the invention will be describedonly with reference to a 1/3 beacon signal frequency allocation scheme.Those skilled in the art will understand, in view of the descriptionprovided herein, the manner in which other beacon signal frequencyallocation schemes can be achieved using the concepts and principles ofthe invention.

As shown in FIG. 4, all of the sectors in the same cell site use thesame frequency for the beacon signals. For example, sectors α, β and γin cell site 30 all use frequency f₁ for the beacon signals. Likewise,sectors α, β and γ in cell site 31 all use frequency f₂ for the beaconsignals. Likewise, sectors α, β and γ in cell site 32 all use frequencyf₃ for the beacon signals. This is in contrast to the known beaconsignal frequency allocation scheme shown in FIG. 1 in which each sectorin the same cell site uses a different frequency for the beacon signals.Consequently, in accordance with the invention, a lesser number offrequencies need to be reserved for the beacon signals, which means thatmore frequencies are available for other purposes, such as for callertraffic, for example. Thus, the beacon signal frequency allocationmethod of the invention results in improved spectral efficiency.

Furthermore, as described below in detail, in accordance with theinvention, the beacon signals do not have to be continuously broadcast,which results in improved power consumption efficiency over the currentscheme as well as less adjacent channel and/or co-channel interference.In addition, because the beacon signals do not have to be broadcastcontinuously, when a time slot (e.g., t₁) is not being used to broadcasta beacon signal, that time slot can be used for transmitting callertraffic or for other purposes, which also improves spectral efficiency.

FIG. 5 is a functional block diagram of cell site 30 shown in thediagram of FIG. 4. The cell site 30 includes beacon logic 60 configuredto generate beacon signals. The beacon logic 60 may be configured togenerate BCCH signals that include a beacon signal that is transmittedin a BCCH time slot (e.g., time slot t₁) using frequency f₁. However, itshould be noted that it is not necessary that the beacon signals betransmitted in a BCCH time slot. The cell site 30 also includes networktraffic logic 55 configured to generate user signals, i.e., callertraffic, which may include voice or data signals. The signals generatedby logic components 55 and 60 are combined and distributed to antennas41, 42 and 43 by signal combining and distributing unit 50. A knownsignal combining and distributing unit, such as that shown in FIG. 2,for example, may be used for this purpose. The signals are thenbroadcast over the respective α, β and γ sectors by the respectivesector antennas 41, 42 and 43.

In the cell site configuration shown in FIG. 5, directional antennas 41,42 and 43 are used to transmit the respective signals over therespective sectors with high directionality to prevent or reduceinterference between signals transmitted over adjacent sectors. Such adirectional configuration reduces the likelihood of adjacent channelinterference and co-channel interference. The manner in which this isaccomplished is described below in detail with reference to FIGS. 6-8.It should be noted that the invention does not require that directionalantennas be used for the sectors of the cell sites. A singleomni-directional antenna could be used for each cell site.

In the exemplary embodiment shown in FIG. 5, it is assumed that a totalof fifteen frequencies are available for use as beacon signalfrequencies and user traffic frequencies. Only frequency f₁ is used forthe beacon signal for cell site 30. Therefore, in this example, fourteenfrequencies, namely frequencies f₂ through f₁₅, are available for usefor caller traffic. For exemplary purposes, the traffic logic 55 isshown as using these fourteen frequencies for caller traffic, although agreater or lesser number of frequencies may be used for this purpose inaccordance with the invention. The invention is not limited with respectto the number of beacon signal frequencies or user signal frequenciesthat are used. The invention also is not limited to any particularnumber of sectors per cell site.

It can be seen from a comparison of FIGS. 2 and 5 that frequencies f₂through f₁₂, which are used as beacon signal frequencies by cell site 1shown in FIG. 2, are available for use as caller traffic frequencies bycell site 30 of the invention shown in FIG. 5. This is because, inaccordance with the invention, a single frequency (e.g., f₁) is used forthe beacon signals for all of the sectors of the cell site 30. Cellsites 31 and 32 shown in FIG. 4 may have configurations that areidentical to the configuration for cell site 30 shown in FIG. 5. Cellsites 31 and 32 use frequencies f₂ and f₃, respectively, for the beaconsignals. Therefore, cell sites 31, 32 and 33 each may use frequencies f₄through f₁₅ for caller traffic. This is a very large improvement inspectral efficiency over the known frequency allocation schemerepresented by FIG. 1 in which frequencies f₁ through f₁₂ are used forthe beacon signals.

In accordance with the invention, beacon signals of a cell site use thesame frequency and are distributed to the different sectors of the cellsite in different time slots. Because a beacon signal is onlytransmitted to one sector at any given time, co-channel and adjacentchannel interference are reduced for both BCCH carriers and trafficcarriers. FIG. 6 illustrates the distribution of beacon signals tosectors α, β and γ of cell site 30 shown in FIG. 5. All of the sectorsof cell site 30 use frequency f₁ for the beacon signals. As shown inFIG. 6, the beacon signal for sector α is transmitted during time slott₀. The beacon signal for sector β is transmitted during time slot t₁.The beacon signal for sector γ is transmitted during time slot t₂. Thebeacon signals may then repeat. For example, the beacon signals forsectors α, β and γ may be retransmitted in time slots t₃, t₄ and t₅,respectively, and so on. The beacon logic 60 (FIG. 5) controls the timeslot allocation and the timing of transmission of the beacon signals.Because the beacon signals for different sectors of a given cell siteare transmitted at different times, the possibility of interferencebetween the beacon signals for different sectors of the same cell isreduced or eliminated.

In accordance with the preferred embodiment, the beacon signals fordifferent sectors of the same cell site are differentiated from eachother by assigning them different sector identifiers (sector IDs). Forexample, each of the beacon signals for sectors α, β and γ of cell site30 is transmitted along with a respective sector ID. Each cell site isassigned a cell site ID that preferably is transmitted along with thebeacon signal, although it could be transmitted separate from the beaconsignal. The mobile devices use the sector IDs to differentiate betweenthe beacon signals of the different sectors. The present invention isalso consistent with e-location or E-911 solutions commonly used toallow mobile devices to be located within a particular sector of aparticular cell site.

Preferably, frequency hopping is used to transmit caller traffic. Forexample, when caller traffic is being transmitted by antenna 41 (FIG. 5)over sector α using frequency f₄ during a time slot t₀, caller trafficis not being transmitted over sectors β and γ using the same frequencyf₄ in the same time slot t₀. Instead, during time slot t₀, callertraffic may be transmitted over sectors β and γ using frequencies f₅ andf₆, respectively. Then, when caller traffic is being transmitted oversector β using frequency f₅ during time slot t₁, for example, callertraffic may be transmitted over sectors α and γ during time slot t₁using frequencies f₄ and f₆, respectively. This frequency hoppingtechnique is generally the same as that described above for the knownconfiguration shown in FIG. 2.

The frequencies that are used for caller traffic (f₄-f₁₅) may be placedin a pool for use by all of the cell sites. In the case where the callertraffic frequencies are placed in a pool and used by all of the cellsites, the frequencies are allocated to time slots in a manner thatprevents or reduces adjacent channel and co-channel interference.Alternatively, the frequencies may be divided into groups for differentcell sites. For example, frequencies f₄-f₇ may be allocated to cell site30, frequencies f₈-f₁₁ may be allocated to cell site 31, and frequenciesf₁₂-f₁₅ may be allocated to cell site 32.

It should be noted that when respective directional antennas are usedfor the respective sectors of a given cell site, it is not alwaysnecessary to use frequency hopping because the directionality of theantennas may be sufficient to prevent interference between the usersignals transmitted using the same frequencies in sectors of the samecell site.

Preferably, beacon signal hopping in the time domain is used to transmitthe beacon signals over different sectors of a cell site using the samefrequency. This can be seen from the timing chart shown in FIG. 7, whichdemonstrates an example of the manner in which three frames of beaconsignals are transmitted sequentially over three different sectors of acell site using the same frequency in accordance with the invention. Inaccordance with this example, each beacon signal is made up of eighttime slots, t₀ through t₇. In time slots t₀, t₁ and t₂, the followingoccurs: the beacon signals corresponding to frame 1 are transmitted oversectors α, β and γ, respectively; the beacon signals corresponding toframe 2 are transmitted over sectors γ, α and β, respectively; and thebeacon signals corresponding to frame 3 are transmitted over sectors β,γ and α, respectively. Transmission over the sectors is then repeated inthe same sequence for the next three time slots. Specifically, in timeslots t₃, t₄ and t₅, the following occurs: the beacon signalscorresponding to frame 1 are transmitted over sectors α, β and γ,respectively; the beacon signals corresponding to frame 2 aretransmitted over sectors γ, α and β, respectively; and the beaconsignals corresponding to frame 3 are transmitted over sectors β, γ andα, respectively. Likewise, in time slots t₆, t₇ and t₈, the followingoccurs: the beacon signals corresponding to frame 1 are transmitted oversectors α, β and γ, respectively; the beacon signals corresponding toframe 2 are transmitted over sectors γ, α and β, respectively; and thebeacon signals corresponding to frame 3 are transmitted over sectors β,γ and α, respectively.

In synchronized networks it is preferable to use the sequential beaconsignal hopping method described above with reference to FIG. 7 becausesequential beacon signal hopping in such cases will significantly reduceadjacent channel and co-channel interference. Synchronized networks arenetworks in which all like sectors for all cell sites are transmittedsimultaneously (e.g., all a sectors for all cell sites are transmittedsimultaneously, all β sectors for all cell sites are transmittedsimultaneously, and all y sectors are transmitted simultaneously). Withthe sequential hopping pattern shown in FIG. 7, the beacon signal istransmitted to each sector the same number of times over any multiple of3×N time slots, where N is a positive integer. For each frame, thebeacon signal for each sector is activated two to three times.Allocating the beacon signals generally evenly among the sectors ensuresthat mobile devices will be able to detect the beacon signals.

In networks that are not synchronized (i.e., networks in which likesectors are not transmitted simultaneously), it may be preferably to usetime domain random beacon signal hopping, as demonstrated by the timingchart shown in FIG. 8. Random beacon signal hopping in the time domainwill generally result in reduced adjacent channel and co-channelinterference as well as improved interference diversity gain. As shownin FIG. 8, for each frame, the order in which the sectors aretransmitted is not sequential. Rather, the order is random. For example,for the beacon signal corresponding to frame 1, sectors α, β and γ aretransmitted in time slots t₀, t₁ and t₂, respectively, but sectors β, αand γ are transmitted in time slots t₃, t₄ and t₅, respectively. Itshould be noted, however, that no sector is transmitted for any of theframes more than once in any given time slot.

Beacon signal time domain hopping patterns other than those shown inFIGS. 7 and 8 may also be used. In some cases, it may be desirable toallocate the beacon signals for the different sectors unevenly, such asin cases where the traffic load is heavier in some sectors than inothers. In such cases, the sectors that are experiencing heavier trafficmay be allocated more beacon signal time slots whereas sectors that areexperiencing lighter traffic may be allocated less beacon signal timeslots. This feature of the present invention provides for traffic loadbalancing in the network. In addition, this feature allows time slotsthat are not being used for transmission of the beacon signal to be usedfor other purposes, such as for caller traffic.

Furthermore, if most or all of the time slots for a given frequency arereserved for the beacon signal, it is not necessary for the beaconsignal to be transmitted at constant power because the beacon signal isbeing transmitted with sufficient frequency to be detected by mobiledevices even at reduced power levels. For example, for every four beaconsignals transmitted to sector α of a given cell site, the first beaconsignal may be transmitted at maximum power, the second beacon signal ata power level that is 2 decibels (dB) below the power level of the firstbeacon signal, the third beacon signal at a power level that is 2 dBbelow the power level of the second beacon signal, and the fourth beaconsignal at a power level that is 2 dB below the power level of the thirdbeacon signal. Therefore, the present invention allows power consumptionto be controlled. This is in contrast to the known beacon signalfrequency allocation scheme, which keeps the beacon signals continuouslyactivated at constant power.

It can be seen from the foregoing that the invention provides severaladvantages over the known beacon signal frequency allocation technique,including, for example, simplified frequency reuse planning, improvedspectral efficiency, reduced adjacent channel and co-channelinterference, and control over power consumption.

FIG. 9 illustrates a flow chart of the method of the invention inaccordance with the preferred embodiment for performing beacon signalhopping in the time domain in a given cell site having multiple sectors.For this example, it will be assumed that each cell site is divided intoat least first and second sectors and that at least one beacon signaltime slot is allocated to each sector. First, time slots of the beaconsignal are allocated to one or more sectors of the cell site, asindicated by block 71. It will be assumed for exemplary purposes thateach sector is allocated at least one beacon signal time slot, althoughthis is not necessary to the invention. As described above, it may bedesirable to allocate more time slots to certain sectors than to others.Next, the beacon signal is transmitted to one of the sectors during timeslot t₁, as indicated by block 72. Next, the beacon signal istransmitted to the other of the sectors in time slot t₂, as indicated byblock 73. Time slot t₂ occurs later in time than time slot t₁, but doesnot necessarily immediately follow time slot t₁ in time.

With reference again to FIG. 5, the beacon signal logic 60 is shownbeing coupled to the signal combining and distribution unit 50, whichcombines the beacon signal with the traffic signal for transmission overthe corresponding one of the sector antennas 41, 42 or 43. It is notnecessary for the beacon signal to be combined with the traffic signal.FIG. 10 shows an alternative embodiment of cell site 30 that enables thebeacon signal to bypass the combining and distribution unit 50. Theembodiment shown in FIG. 10 is essentially identical to the embodimentshown in FIG. 5 except that the beacon logic 100 is coupled to aseparate beacon signal transmitter 110 and a three panel directionalantenna 120 having panels pointed at sectors α, β and γ. The cell site30 represented by the block diagram of FIG. 10 performs the samefunctions as those performed by the cell site 30 represented by theblock diagram of FIG. 5. Therefore, the components shown in FIG. 10 ashaving the same reference number as components shown in FIG. 5 will notbe described.

It should be noted that while the present invention has been describedwith reference to certain exemplary embodiments, the present inventionis not limited to the embodiments described herein. For example, FIG. 5shows respective directional antennas being used for respective timeslots. A single omni-directional antenna may be used for transmission ofthe beacon signals over all of the sectors of the cell site, although itis preferred to use respective directional antennas for the respectivecell site sectors. Also, a dedicated antenna may be used for the beaconsignals so that the beacon signals would not have to be combined anddistributed by the combining and distribution unit 50 (FIG. 5). Itshould also be noted that although a single frequency may be used forthe beacon signals for all of the sectors of a cell site, it is notnecessary that a single frequency be used. The time domain beacon signalhopping method of the invention also applies to cases where multiplefrequencies are used for different sectors of a cell site. Othermodifications may be made to the embodiments described herein and allsuch modifications are within the scope of the invention.

1. An apparatus for transmitting beacon signals over a cell site of awireless communications network, the cell site being divided into atleast a first sector a and a second sector 13, the apparatus comprising:beacon signal logic configured to allocate at least a first beaconsignal time slot t₁ to at least the first sector a; and a transmitter,the transmitter transmitting a first beacon signal on a first beaconsignal frequency f₁ over the first sector a during the first beaconsignal time slot t_(i).
 2. The apparatus of claim 1, wherein the beaconsignal logic is configured to allocate at least a second beacon signaltime slot t₂ to the second sector 13, wherein time slot t₂ occurs laterin time than time slot t₁, the transmitter transmitting a second beaconsignal on the first beacon signal frequency f₁ over the second sector pduring time slot t2.
 3. The apparatus of claim 2, wherein when the firstbeacon signal is being transmitted over the first sector a during timeslot t₁, the second beacon signal is not being transmitted over thesecond sector p and when the second beacon signal is being transmittedover the second sector P during time slot t₂, the first beacon signal isnot being transmitted over the first sector a.
 4. The apparatus of claim3, further comprising: a combining and distribution unit that combinesthe beacon signals being carried on frequency f₁ with at least onecaller traffic signal being carried on at least one user carrierfrequency f₄, the transmitter transmitting the respective beacon signalsalong with the caller traffic signal over the respective cell sitesectors.
 5. An apparatus for transmitting beacon signals over a cellsite of a wireless communications network, the cell site being dividedinto at least a first a, a second sector p, and a third sector y, theapparatus comprising: beacon signal logic configured to allocate atleast a first beacon signal time slot t₁ to the first sector a, a secondbeacon signal time slot t₂ to the second sector 13, and a third beaconsignal time slot t₃ to the third sector y; and a transmitter, thetransmitter transmitting a first beacon signal on a first beacon signalfrequency f₁ over the first sector a during time slot t₁, a secondbeacon signal on the first beacon signal frequency f₁ over the secondsector 13 during the second time slot t₂, and a third beacon signal onthe first beacon signal frequency f₁ over the first sector y during thethird time slot t₃, wherein time slot t₂ occurs later in time than timeslot t₁ and time slot t₃ occurs later in time than time slot t₂.
 6. Theapparatus of claim 5, wherein when the first beacon signal is beingtransmitted over the first sector a during time slot t₁, the secondbeacon signal is not being transmitted over the second sector f3 andwhen the second beacon signal is being transmitted over the secondsector 13 during time slot t₂, the first beacon signal is not beingtransmitted over the first sector a.
 7. The apparatus of claim 6,wherein when the second beacon signal is being transmitted over thesecond sector 13 during time slot t₂, the third beacon signal is notbeing transmitted over the third sector y and when the third beaconsignal is being transmitted over the third sector y during time slot t₃,the second beacon signal is not being transmitted over the second sector13, and wherein when the first beacon signal is being transmitted overthe first sector a during time slot t₁, the third beacon signal is notbeing transmitted over the third sector y and when the third beaconsignal is being transmitted over the third sector y during time slot t₃,the first beacon signal is not being transmitted over the first sectora.
 8. The apparatus of claim 7, wherein the beacon signal logic isconfigured to allocate at least a fourth beacon signal time slot t₄ tothe first sector a, a fifth beacon signal time slot t₅ to the secondsector 13 and a sixth beacon signal time slot t₆ to the third sector y,wherein time slot t₆ occurs later in time than time slot t₆, time slott₅ occurs later in time than time slot t₄, and time slot t₄ occurs laterin time than time slot t₃, the transmitter transmitting a fourth beaconsignal on the first beacon signal frequency f₁ over the second sector aduring time slot t₄, a fifth beacon signal on the first beacon signalfrequency f₁ over the second sector 13 during time slot t₅, and a sixthbeacon signal on the first beacon signal frequency f₁ over the thirdsector y during time slot t6.
 9. The apparatus of claim 8, wherein timeslot t₂ begins when time slot t₁ ends and ends when time slot t₃ begins,and wherein time slot t₃ begins when time slot t₂ ends and ends whentime slot t₄ begins, and wherein time slot t₄ begins when time slot t₃ends and ends when time slot t₅ begins, and wherein time slot t₆ beginswhen time slot t₅ ends.
 10. The apparatus of claim 9, wherein when thefourth beacon signal is being transmitted over the first sector a duringtime slot t₄, the fifth beacon signal is not being transmitted over thesecond sectorp and when the fifth beacon signal is being transmittedover the second sector (3 during time slot t₅, the fourth beacon signalis not being transmitted over the first sector a, and wherein when thefifth beacon signal is being transmitted over the second sector (3during time slot t₆, the sixth beacon signal is not being transmittedover the third sector y, and when the sixth beacon signal is beingtransmitted over the sixth sector y during time slot t₆, the fifthbeacon signal is not being transmitted over the second sector (3. 11.The apparatus of claim 5, wherein the beacon signal logic is configuredto allocate at least a fourth beacon signal time slot t₄ to the firstsector a, a fifth beacon signal time slot t₅ to the second sector p anda sixth beacon signal time slot t₆ to the first sector a, wherein timeslot t₆ occurs later in time than time slot t₆, time slot t₅ occurslater in time than time slot t₄, and time slot t₄ occurs later in timethan time slot t₃, the transmitter transmitting a fourth beacon signalon the first beacon signal frequency f_(i) over the second sector aduring time slot t₄, a fifth beacon signal on the first beacon signalfrequency f₁ over the second sector (3 during time slot t₆, and a sixthbeacon signal on the first beacon signal frequency f₁ over the firstsector a during time slot t₆.
 12. An apparatus for transmitting beaconsignals over a cell site of a wireless communications network, the cellsite being divided into at least a first sector a, a second sector 13,and a third sector y, the apparatus comprising: beacon signal logicconfigured to sequentially allocate beacon signal time slots to thefirst sector a, the second sector ₁₃ and the third sector y; and atransmitter, the transmitter transmitting beacon signals on a firstbeacon signal frequency f₁ over the first sector a, the second sector (3and the third sector y during respective time slots, wherein when thebeacon signal is being transmitted over sector a, the beacon signal isnot being transmitted over sectors 13 or y, and when the beacon signalis being transmitted over sector 13, the beacon signal is not beingtransmitted over sectors a or y, and when the beacon signal is beingtransmitted over sector y, the beacon signal is not being transmittedover sectors 13 or a.